The present invention relates to a portable apparatus for aligning the axles of a vehicle, such as a tractor or trailer, and for detecting bends, bows, twists and other irregularities in vehicle frames and other components. The invention allows mechanics to repair and replace frames and other major structural components of vehicles in the field, without the aid of special purpose, precision-leveled racks and platforms.
In a tractor-trailer combination, the trailer will sometimes fail to properly trail the tractor because of axle misalignment. This problem generally results from the axle being misaligned such that it is not perpendicular to a fore-and-aft centerline of the frame of the trailer. Similar misalignments of the rear axle(s) of the tractor can also cause problems, such as accelerated tire wear, lowered fuel economy, and increased driver fatigue.
Various methods for providing vehicle axle correction have been proposed. U.S. Pat. No. 3,566,476 to McWhorter uses a light projector attached on a support behind the wheel axle. The projector is first directed towards a rear reference point extending from the underside of the trailer frame. The projector is then tilted downwardly and the beam projected forwardly to a front reference point attached to a kingpin. The beam will supposedly miss the kingpin reference point when the axle is out of alignment. Both the kingpin reference point and the rear reference point are located on the centerline of the trailer frame. The light projector is connected on a frame to two wheel gauges which are attached around the circumference of the tire. This arrangement suffers from being sensitive to tire size and wear, the regularity of the underlying ground surface, and other factors so that an inaccurate measurement of the misalignment of the axle may result. Also, since the projector is fixed along the centerline, the most accurate measurement of misalignment may not be possible since the deviation from true alignment is greatest on the adjusting side (as opposed to the stationary side) of the vehicle axle, and the deviation will therefore be greater on the adjusting side of the centerline than at the centerline. Thus, a measurement of misalignment made on the adjusting side of the axle will allow for increased resolution, when compared to a measurement made on the centerline or on the stationary side of the axle.
Another problem that has been noticed in devices such as that shown in U.S. Pat. No. 3,566,476 to McWhorter (i.e., devices which use a light projector attached on a support), is the relative ease with which the beam of light can deviate from a perpendicular relationship to the support and consequently the wheel axle. A minute deviation from the perpendicular arrangement of the light to the axis of the support, such as might result from normal tolerances in the support structure or light source enclosure, or by external forces acting on the support or light source enclosure, may cause a relatively large deviation and error at the target connected to the far end of the frame. Since the range of misalignment of an axle is normally measured in fractions of an inch, a slight deviation of the light beam from perpendicularity with the support (and wheel axle) will cause an erroneous measurement of axle alignment.
In addition to the alignment of vehicle axles, mechanics who maintain and repair large vehicles, such as tractors and trailers, are often called upon to replace components of the undercarriage, straighten or rebuilt frames, and otherwise repair damage caused by road collisions, extended usage, or material failures. To properly perform such repairs often requires the use of precision leveled working surfaces or other special tools and conditions to ensure that the rebuilt or repaired vehicle is serviceable. The present invention provides an arrangement for making such repairs which is convenient and relatively inexpensive, while maintaining the required degree of precision.
An object of the present invention is to provide an apparatus for aligning wheel axles of and making other repairs to a vehicle, which apparatus is both accurate and simple to operate.
Another object of the present invention is to provide an apparatus for aligning wheel axles of and making other repairs to a vehicle, which can be used on uneven ground.
Yet another object of the present invention is to provide such a device which is portable and which can be used in various surroundings and under various conditions.
A further object of the present invention is to provide a device which measures directly from the central axis of the wheel axle so that irregularities in the ground surface do not effect the measurement of wheel axle alignment.
A further object of the present invention is to provide a device for establishing a reference plane underneath the frame of a tractor or trailer so that measurements can be made between this reference plane and the vehicle, for providing an indication of irregularities in the frame of the vehicle.
A still further object of the present invention is to provide an apparatus for aligning the axles of a tractor which measures the alignment at different points along a line that is exactly parallel to the center axis of a wheel axle.
A still further object of the present invention is to provide a device which assures perpendicularity of a generated beam of light to a central axis of a support of the light source.
These and other objects of the present invention are achieved in a device for establishing a reference plane with respect to a vehicle frame from which measurements relating to the vehicle can be made and which includes a first target assembly attachable to the underside of the vehicle frame. This first target assembly has at least two targets spaced apart on a first line which is substantially transverse to the vehicle frame. The individual targets of the assembly are spaced an equal vertical distance from the underside of the frame. A second target assembly, which is attachable to the underside of the vehicle frame, also has at least two targets spaced apart on a second line which is substantially transverse to the vehicle frame. Each of these individual targets are also spaced the same vertical distance from the underside of the vehicle frame, and these targets are provided with openings for allowing a light beam to pass through. A light source directs a beam of light through an individual target of the second target assembly toward a corresponding target on the first assembly. This light source is positionable along a line that is substantially transverse to the vehicle frame.
An advantage of this embodiment of the present invention is that a reference plane is established with respect to a vehicle frame by the multiple targets on the target assemblies. From this reference plane, measurements can be made to various points on the underside of the vehicle frame to detect irregularities, so that steps can be taken to correct these irregularities. A light source, which is positionable along a line substantially transverse to the vehicle frame, is used in combination with the multiple targets to define the reference plane beneath the vehicle so as to allow measurements to be made relative to the frame at any point.
Advantageous features are achieved by certain preferred embodiments of the present invention which include a U-shaped frame having a horizontal bar and two upright portions extending from the bar at right angles thereto. The upright portions include means for attaching the U-shaped frame to a central axis of the axle such that the horizontal bar is parallel to the central axis. A first target assembly is attachable to an underside of the vehicle, and has at least two targets spaced apart on a first line substantially transverse to the long axis of the vehicle and spaced an equal vertical distance from the underside of the vehicle. A second target assembly, which is also attachable to the underside of the vehicle, has at least two targets spaced apart on a second line substantially transverse to the long axis of the vehicle. The targets on the second target assembly are each spaced the same vertical distance from the vehicle underside, and are provided with openings for allowing a light beam to pass through the targets. Finally, a light source, for generating a beam of light, is slidably mounted on the horizontal bar of the U-shaped frame. This light source is slidably positionable to a plurality of points along the horizontal bar.
In the arrangements according to these preferred embodiments, very accurate alignment is provided since each of the target assemblies includes at least two targets so that the alignment can be measured at the adjusting side of the axle, as opposed to the center or stationary side of the axle. Since the axle effectively "pivots" about the stationary side, any deviation from perfect alignment at the adjusting side will be greater than at the center and still greater than at the stationary side, and thus, easier to detect and correct.
In some preferred embodiments, a perpendicularity checking device assures that the beam of light produced by the light source is perpendicular to the horizontally extending bar. This eliminates error which can be introduced into the measurements if the light beam produced by the source is not truly perpendicular to the horizontal bar of the frame which supports the light. Deviations from a truly perpendicular arrangement can result from normal tolerances in the light source support, especially in such supports which provide for horizontal and/or vertical movements of the light source. In order to allow for such movements, clearances must be provided in the mechanical parts of the support, and these clearances can result in variance of the light beam from a truly perpendicular orientation with respect to the horizontal bar of the frame. The light source itself may also be a source of error in this regard. The light source which is preferably used in this and other wheel alignment systems is a relatively low priced, low powered laser. The laser is mounted in a relatively lightweight frame which is subsequently attached (for example, by screws or bolts) to the underlying support frame. The inventor has determined that the light beam produced by the laser is not carefully aligned with the associated enclosure, including the brackets or holes provided for attachment to an underlying support, so that replacement of the laser assembly in such an aligning apparatus may introduce significant errors into measurements subsequently made by the apparatus.
In certain other preferred embodiments, objects of the invention are achieved in an apparatus which includes a U-shaped frame having a horizontal bar and two upright portions extending from the bar at right angles thereto. These upright portions include means for attaching the U-shaped frame to a central axis of the wheel axle so that the horizontal bar is parallel to the central axis. The apparatus also includes a frame squaring plate which is attachable to the frame of the vehicle. This squaring plate has at least two reference portions which, in one preferred embodiment, are upright bars. The distances from each of these reference portions to the horizontal bar is measured and compared to determine axle alignment. These preferred embodiments provide a portable apparatus which does not need a light source, yet which still provides an accurate measure of wheel axle alignment. Accurate measurement is assured through the use of a U-shaped frame which has a horizontal bar that is exactly parallel to the central axis of the axle being measured, and which is brought into relatively close proximity to the reference portions of the frame squaring plate.
Other objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, preferred embodiments in accordance with the present invention.